Nonlinear theory of slow cyclotron wave interaction in folded waveguide

Summary form only given, as follows. A three-dimensional nonlinear theory is presented for the generation of broadband radiation from slow cyclotron wave interaction in a folded waveguide. The serpentine structure is formed by folding a rectangular waveguide so that the orientation of the magnetic changes (H-plane bend) instead or the conventional E-plane bend configuration where the orientation of the electric field changes. The H-plane bend structure can use larger beam tunnel without distorting the RF field structure and generate higher output power. Numerical results are shown for the TE/sub 10/ mode propagation in an unridged and a double ridged waveguide. For a 61.5 kV, 3 A beam with /spl alpha/=1.0 and /spl Delta/V/sub Z//V/sub Z/=0, calculations show an efficiency of 25% with 20% bandwidth and an efficiency of 35% at 10% bandwidth. The efficiency and bandwidth is relatively unchanged up to a beam axial velocity spread of 2%. The bandwidth can be further increased by mode coalescing techniques. Multistage operation is necessary to avoid backward wave oscillation.